1. Field of the Invention
The present invention relates to a method for producing an L-amino acid using a microorganism. L-amino acids are used in various applications, such as for use in seasonings, food additives, feed additives, chemicals, and drugs.
2. Brief Description of the Related Art
L-amino acids such as L-threonine and L-lysine are industrially produced by fermentation of bacteria such as Escherichia. Bacterial strains isolated from nature, artificial mutants, and recombinants in which L-amino acid biosynthetic enzymes are enhanced by gene recombination, or the like, are used. Examples of the methods for producing L-threonine include, for example, the methods described in Japanese Patent Laid-open (Kokai) No. 5-304969, International Publication WO98/04715, Japanese Patent Laid-open No. 05-227977, and U.S. Patent Published Application No. 2002/0110876. Examples of the methods for producing L-lysine include, for example, the methods described in Japanese Patent Laid-open No. 10-165180, Japanese Patent Laid-open No. 11-192088, Japanese Patent Laid-open No. 2000-253879, and Japanese Patent Laid-open No. 2001-057896.
In the industrial production of L-amino acids by fermentation, saccharides, such as glucose, fructose, sucrose, blackstrap molasses, starch hydrolysate, and so forth, are used as carbon sources. Other carbon sources that are frequently used in methods for producing an L-amino acid by fermentation include saccharification products of starches derived from higher plants such as corn and cassava. These have a low moisture content and high starch content, and therefore, it is easy to industrially obtain starches from them. On the other hand, although starches in microalgae are usually present in an amount per dry weight unit comparable to that of corn or cassava, the dry weight of the algae per weight unit of culture medium does not approach 1%. The process of separating alga bodies, dehydrating them, disrupting the cells, extracting starches, and purifying the starches is complicated and difficult. Although ethanol fermentation using starches of microalgae is described in U.S. Patent Published Application No. 2006/135308, U.S. Patent Published Application No. 2007/0202582 and Matsumoto, M. et al., 2003, Appl. Biochem. Biotechnol., 105-108:247-254, the results of the ethanol fermentation are not described. Furthermore, examples using saccharified starches of microalgae for amino acid production has not been previously reported.
It is known that Escherichia coli, which is a typical amino acid-producing bacterium, can grow using glycerol as the sole carbon source (Lin, E. C. C., 1996, pp. 307-342, In F. D. Neidhardt (ed.), Escherichia coli and Salmonella Cellular and Molecular Biology/Second Edition, American Society for Microbiology Press, Washington, D.C.), and can grow using long chain fatty acids having 12 or more carbon atoms as the sole carbon source (Clark, D. P. and Cronan Jr., J. E., 1996, pp. 343-357, In F. D. Neidhardt (ed.), Escherichia coli and Salmonella Cellular and Molecular Biology/Second Edition, American Society for Microbiology Press, Washington, D.C.). Therefore, Escherichia coli can assimilate both long chain fatty acids and glycerol, both of which are hydrolysis products of fats and oils. However, Escherichia coli does not have lipase activity, and therefore, it cannot directly assimilate fats and oils (Brenner, D. J. and Farmer III J. J. Family I., 2005, pp. 587-669, In: D. J. Brenner, N. R. Krieg and J. T. Staley, Editors, Bergey's Manual of Systematic Bacteriology, Volume Two: The Proteobacteria Part B: The Gammaproteobacteria, Springer, N.Y.). Furthermore, it is also known that the solubility of long chain fatty acids is generally extremely low, and solubility measurements are described in Vorum, H. et al., 1992, Biochimica et Biophysica Acta, 1126:135-142. However, solubility of lauric acid is not lower than 0.1 g/L, solubility of oleic acid is not higher than 0.0003 g/L, and solubility of palmitic acid is not higher than 0.00000003 g/L. Therefore, it is difficult to simultaneously assimilate highly water-soluble glycerol and aliphatic acids. L-amino acid production based on direct fermentation utilizing an hydrolysate of fats and oils, which is a mixture of long chain fatty acids and glycerol, as the carbon source has not been previously reported.
Soybean and Elaeis guineensis (oil palm) are oil plants generally used for production of edible oils, beans, or fruits thereof. They typically contain about 20% of fats and oils. Microalgae is also know to produce fats and oils, and the amounts produced per area far exceeds that obtained with the oil plants, as reported in Chisti Y., 2007, Biotechnol. Adv., 25:294-306. However, the process of separating algae and alga bodies, dehydrating them, disrupting the cells, extracting fats and oils, and purifying them is complicated and difficult, as in the case of starches. Therefore, L-amino acid production based on direct fermentation utilizing fats and oils from algae has also not been previously reported.